Cometary nuclei are remnants of the early solar system. They contain key
information from the time when planets were forming, and even earlier;
ome contain material from the natal interstellar cloud. The most easily
modified forms of matter-- the ices, low-temperature-refractory organics,
and minerals-- bear special significance for understanding processes
affecting material during its journey from the natal cloud core through the
young planetary system. Comets Hyakutake and Hale-Bopp were the first bright
comets to be studied with powerful new astronomical facilities. A wealth of
new information on cometary organic composition was obtained from them,
including the discovery of symmetric hydrocarbons (methane, ethane, acetylene)
by infrared spectroscopy and of six new molecular species at radio wavelengths.
Since then, larger telescopes (e.g. Keck) and even more powerful instruments
(e.g. NIRSPEC) have become available, driving a revolution in our ability to
characterize native ices. The organic composition of six comets from the
Oort-cloud reservoir (including the unusual disrupted comet C/2000 S4) will be
compared and discussed in the context of heterogeneity in the giant-planets'
nebular region. Implications for future studies of Oort-cloud and
Jupiter-family comets will be mentioned.